Free Newsletters - Space News - Defense Alert - Environment Report - Energy Monitor
. 24/7 Space News .




TECTONICS
Earth's crust was unstable in the Archean eon and dripped down into the mantle
by Staff Writers
Mainz, Germany (SPX) Dec 31, 2013


Just another bad day during the early times of primordial Earth. A computer simulation image of the process can be seen here.

Earth's mantle temperatures during the Archean eon, which commenced some 4 billion years ago, were significantly higher than they are today. According to recent model calculations, the Archean crust that formed under these conditions was so dense that large portions of it were recycled back into the mantle.

This is the conclusion reached by Dr. Tim Johnson who is currently studying the evolution of the Earth's crust as a member of the research team led by Professor Richard White of the Institute of Geosciences at Johannes Gutenberg University Mainz (JGU). According to the calculations, this dense primary crust would have descended vertically in drip form.

In contrast, the movements of today's tectonic plates involve largely lateral movements with oceanic lithosphere recycled in subduction zones. The findings add to our understanding of how cratons and plate tectonics, and thus also the Earth's current continents, came into being.

Because mantle temperatures were higher during the Archean eon, the Earth's primary crust that formed at the time must have been very thick and also very rich in magnesium. However, as Johnson and his co-authors explain in their article recently published in Nature Geoscience, very little of this original crust is preserved, indicating that most must have been recycled into the Earth's mantle.

Moreover, the Archean crust that has survived in some areas such as, for example, Northwest Scotland and Greenland, is largely made of tonalite-trondhjemite-granodiorite complexes and these are likely to have originated from a hydrated, low-magnesium basalt source.

The conclusion is that these pieces of crust cannot be the direct products of an originally magnesium-rich primary crust. These TTG complexes are among the oldest features of our Earth's crust. They are most commonly present in cratons, the oldest and most stable cores of the current continents.

With the help of thermodynamic calculations, Dr. Tim Johnson and his collaborators at the US-American universities of Maryland, Southern California, and Yale have established that the mineral assemblages that formed at the base of a 45-kilometer-thick magnesium-rich crust were denser than the underlying mantle layer.

In order to better explore the physics of this process, Professor Boris Kaus of the Geophysics work group at Mainz University developed new computer models that simulate the conditions when the Earth was still relatively young and take into account Johnson's calculations.

These geodynamic computer models show that the base of a magmatically over-thickened and magnesium-rich crust would have been gravitationally unstable at mantle temperatures greater than 1,500 to 1,550 degrees Celsius and this would have caused it to sink in a process called 'delamination'. The dense crust would have dripped down into the mantle, triggering a return flow of mantle material from the asthenosphere that would have melted to form new primary crust.

Continued melting of over-thickened and dripping magnesium-rich crust, combined with fractionation of primary magmas, may have produced the hydrated magnesium-poor basalts necessary to provide a source of the tonalite-trondhjemite-granodiorite complexes. The dense residues of these processes, which would have a high content of mafic minerals, must now reside in the mantle.

Publication: Tim E. Johnson et al., Delamination and recycling of Archaean crust caused by gravitational instabilities, Nature Geoscience, 1 December 2013 DOI:10.1038/ngeo2019

.


Related Links
JGU Geophysics and Geodynamics Group
Tectonic Science and News






Comment on this article via your Facebook, Yahoo, AOL, Hotmail login.

Share this article via these popular social media networks
del.icio.usdel.icio.us DiggDigg RedditReddit GoogleGoogle




Memory Foam Mattress Review
Newsletters :: SpaceDaily :: SpaceWar :: TerraDaily :: Energy Daily
XML Feeds :: Space News :: Earth News :: War News :: Solar Energy News





TECTONICS
Rising mountains dried out Central Asia
Stanford CA (SPX) Dec 17, 2013
A record of ancient rainfall teased from long-buried sediments in Mongolia is challenging the popular idea that the arid conditions prevalent in Central Asia today were caused by the ancient uplift of the Himalayas and the Tibetan Plateau. Instead, Stanford scientists say the formation of two lesser mountain ranges, the Hangay and the Altai, may have been the dominant drivers of climate in ... read more


TECTONICS
Wake Up Yutu

Chang'e 3 Lander and Rover From Above

Chang'e-3 satellite payload APXS obtained its first spectrum of lunar regolith

China's moon rover "sleeps" through lunar night

TECTONICS
More than 1,000 chosen for one-way Mars reality-TV mission

'Mars One' will reveal if there is life outside Earth

Clues from Orbit Aiding Exploration Of Opportunity Rover

Decade-Old Rover Adventure Continues on Mars and Earth

TECTONICS
Only lawyers profit as tech giants go to war over patents

Astronauts Practice Launching in NASA's New Orion Spacecraft

Space trips open to Chinese travelers

Work on NASA's New Orion Spacecraft Progresses as Engineers Pivot to 2014

TECTONICS
China launches communications satellite for Bolivia

China's moon rover continues lunar survey after photographing lander

China's Yutu "naps", awakens and explores

Deep space monitoring station abroad imperative

TECTONICS
CU-Boulder to fly antibiotic experiment on ants to space station

Station Cosmonauts Complete Spacewalk to Deploy Cameras

Antares and Cygnus Launch Update

Expedition 38 Sends New Year's Greetings on Off-Duty Day

TECTONICS
Antares Launch Scheduled For Jan 7

Russian Rocket Puts Telecoms Satellite Into Orbit

The Athena-Fidus satellite is readied for Arianespace first heavy-lift mission of 2014

Boeing, Energia Achieve Mixed Results in Counterclaims

TECTONICS
NASA's Hubble Sees Cloudy Super-Worlds With Chance for More Clouds

Researchers use Hubble Telescope to reveal cloudy weather on alien world

Using an Atmosphere to Weigh a Planet

Gaia Mission Could Help Map Exoplanets

TECTONICS
Throwing out the textbook: Salt surprises chemists

3D-printed components flown in British fighter jet

Mission to test laser communications across space distances a success

Large-aperture planar lens antennas with gradient refractive index




The content herein, unless otherwise known to be public domain, are Copyright 1995-2014 - Space Media Network. AFP, UPI and IANS news wire stories are copyright Agence France-Presse, United Press International and Indo-Asia News Service. ESA Portal Reports are copyright European Space Agency. All NASA sourced material is public domain. Additional copyrights may apply in whole or part to other bona fide parties. Advertising does not imply endorsement,agreement or approval of any opinions, statements or information provided by Space Media Network on any Web page published or hosted by Space Media Network. Privacy Statement